Cara Delevingne and St Vincent during London fashion week at Kensington Gardens in September 2015.
Photograph: David M Benett/Getty

Kristen Stewart, the actor, is photographed at Cannes holding hands with her ex-girlfriend Alicia Cargile. Supermodel Cara Delevingne kisses her girlfriend, the singer St Vincent, on the front row at London fashion week. Seventeen-year-old Hunger Games actor Amandla Stenberg uses the Teen Vogue Snapchat account to describe how “bruising” it has been “fighting against my identity as a black bisexual woman”. Model, DJ and actor Ruby Rose describes herself as “very gender fluid”, adding: “I feel more like I wake up every day sort of gender neutral.”

Twenty years ago these stories would have been accompanied by prurient “oohs” and much vivid speculation over what message these women were trying to send. Today such moments are everywhere, a sign that increasingly we define ourselves in less structured, more mutable ways.

And nowhere is that more true than within the millennial generation. Last week a survey of 33,728 Americans published in the journal Archives of Sexual Behaviour stated that there had been a huge increase in the number of people reporting same-sex experiences, and alongside this, a greater acceptance of people’s sexuality. The study concluded that 49% of all adults and 63% of millennials “expressed tolerance of these relationships”.

“It’s clear that people under a certain age are much more comfortable not just with same-sex relationships but with bisexuality, gender-fluidity and all sorts of other ways of living that fall outside the traditional binaries of straight and gay, male and female,” says journalist Laurie Penny, who describes herself as bisexual and genderqueer.

“That’s partially down to the internet and the way it’s allowed more visibility for people who have life experiences outside the norm. It provides a way for people to congregate and talk about issues that matter to them.”

Penny adds that the growing number of celebrities either in same-sex relationships or willing to discuss their gender in non-binary terms is helping to change attitudes. “I didn’t talk about being bisexual or genderqueer much in public before last year, because I was facing so much online harassment as it was that I just didn’t have the energy to have that conversation as well.

“One thing that made it easier, silly as it sounds, was Miley Cyrus, and Ruby Rose, and others like them, coming out as genderqueer or gender-fluid. That made it less of a big deal to say it myself. Celebrities can provide a language for people. It allows them to see their own experiences reflected.”

When I came out in 2007/2008, I frequently had homophobic abuse thrown at me in Dublin but that’s extremely unlikely now

Niamh Ni Mhaoileoin, editor of political blog Left Foot Forward, who identifies as queer, agrees that the more we see well-known people living their lives openly, the more things will change. “Kristen Stewart is an interesting one because initially there was a lot of covert talk about her ‘gal pals’, so I think there is still an issue with ‘bi-erasure’. That said, it’s powerful to have these images because the message they send is that being gay can just be a part of your life – it doesn’t have to dominate it.

Ni Mhaoileoin, 27, says she is “blown away” by how much perception of sexuality has changed. “When I came out in 2007-2008, I frequently had homophobic abuse thrown at me in Dublin, but that’s extremely unlikely now. Among the younger generation there’s just more fluidity and more willingness to just not even ask the question. My experience is that older people are more likely to say ‘so you were with a man, now you’re with a woman, what’s going on there?’, whereas younger people will just nod. It’s not an issue.”

Yet as parts of society move towards a more progressive agenda, others are becoming more entrenched. In North Carolina, governor Pat McCrory infamously signed a bill banning transgender people from bathrooms that don’t match the sex they were assigned at birth. Transgender people are more likely to suffer violent attacks and discrimination in the workplace.

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“It’s important to note that it’s not as simple as [saying] we are all becoming more tolerant and accepting,” says Penny. “There is still a great deal of prejudice against trans, queer and gender non-conforming people, and while certain gains have been made, it’s still not easy.”

Certainly it was notable that, amid the furore over Amber Heard’s divorce from Johnny Depp, her bisexuality became a stick for commentators to beat her with as various outlets suggested her sexuality was in some way to blame for the marriage’s acrimonious collapse.

“Once the chips were down, that stuff was very quickly used against her,” says Poppy Steward, a 24-year-old payroll administrator from Poole in Dorset, who identifies as bisexual.

“Amber Heard’s bisexuality was fine when people could feel that she’d made her choice and got married to a man, but once that marriage fell apart then suddenly the conversation is all about how she’s a mean person who’s somehow going to ruin the world with her nasty bisexuality.”

Steward says this chimes with her own experiences. “When people find out I’m bisexual, it’s all ‘oh, that’s cool, I’m open-minded, it’s the 21st century and we’re all progressive here’ – but when it comes up when I’m out with someone I’ve met on OKCupid, then it’s a different story. I’ll tell people on dates that I’m bisexual, and I see the hesitation flicker in their eyes. Even if the next thing they say is ‘oh well, that’s fine’, I’ve still seen them hesitate.”

Twenty-year-old law student Bethany agrees. “While I would say the millennial generation is more open about same-sex relationships and more broadly tolerant about all things they don’t see any harm in, it is also the case that – as someone who broadly identifies as bi – I don’t feel like I’m a part of the LGBTA community, or even that I would necessarily be accepted as part.”

She says: “This is down to having been in a heterosexual relationship for three years. People always assume that means you’re straight. It doesn’t necessarily bother me, and I don’t really feel the need to be ‘out’ and label my sexuality, but sometimes it can be frustrating and leave me feeling constrained, or not taken seriously.”

Kristen Stewart has taken a similarly blurred line. In a recent interview with Nylon magazine she said: “If you feel like you really want to define yourself, and you have the ability to articulate those parameters and that in itself defines you, then do it,” she said, before adding that she believed in fluidity. “Google me, I’m not hiding.”

Steward says: “The more conversations like that we have, the more attitudes will change bit by bit and ripple by ripple.

“The visibility of people like Amber Heard, Kristen Stewart or Rowan Blanchard, the girl from [teen sitcom] Girl Meets World, who identifies as gender-fluid, is important. The thing is, we all want to be progressive, and so if you were clicking on a button in a survey you’d probably say you were open-minded about sexuality and gender – but what about when you’re lying in bed at night, thinking about a potential partner, would you really be so open-minded and progressive then?”

Ni Mhaoileoin agrees. “We’re going in the right direction, but we’ve still got some way to go. There have been some huge changes, but at the same time we can’t afford to be complacent.”

For Penny, our attitudes towards gender and sexuality will only continue to change in the next few years. “There’s been a strong conversation about gender and sexuality online for some time,” she says. “We’ve reached the point where mainstream culture has noticed what’s happening. From here it can only snowball – and I say, bring it on.”

This article was amended on 5 June 2016. In an earlier version the words: “The more conversations like that we have, the more attitudes will change bit by bit and ripple by ripple,” were wrongly attributed to Kristen Stewart. This has been corrected.